Conjugation reactions

ABSTRACT

An initiator for the terminal group of the polymer product of an atom or group radical transfer polymerisation has an activated carboxyl or an amine group which is reacted with an amine or carboxyl (respectively) group containing biologically active compound. The initiator is preferably 4-(3-(2-bromo, 2-methyl-propionate)phenyl)-propionic acid N-hydroxysuccinimide ester or 2-bromo, 2-methyl-propionic acid N-hydroxysuccinimide ester. The monomers preferably comprise a zwitterionic monomer such as 2-methacryloxyethyl-2′-trimethyl ammoniumethyl phosphate inner salt.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of pending U.S. application Ser. No. 10/542,333, which is a National Stage of International Application No. PCT/GB04/00140 filed Jan. 16, 2004, claiming priority based on United Kingdom Application No. 0301014.7, filed Jan. 16, 2003, the contents of all of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to forming conjugates of polymers and biologically active compounds, and to functional polymer precursors therefore.

2. Description of the Related Art

We have described in WO-A 2003/062290 (unpublished at the priority date hereof) the concept of taking a biologically active drug molecule and reacting it with a compund so as to functionalise it with an appropriate brominated moiety. The modified drug is capable of initiating an atom transfer radical polymerisation (ATRP) with monomers such as 2-methacryl-oyloxyethyl-2′-trimethylammonium ethyl phosphate inner salt. The compound 2-bromo-2-methyl propionic acid bromide is one such bromine-functionalising agent, the acid bromide portion reacting with any active hydroxyl group on the drug compound to produce a brominated analogue of a methacrylate moiety that has been shown to be eminently suitable for initiating ATRP (see works of Matyjaszewski, Armes and Haddleton). With this functionalising agent, this reaction is only possible in cases where the drug molecule and the 2-bromo, 2-methyl propionic acid bromide are both soluble in some organic solvent that is not reactive towards the acid bromide. In that specification we also describe a bromine-functionalising agent which is used to acylate an amine group, namely of a protein. The subject matter has a common priority date as claims of the present case and of example 4 herein.

It may be desirable to functionalise large biological entities such as proteins and antibodies with polymers. Roche and Schering-Plough both have on the market successful interferon-based products that have been modified by PEGylation of the biological entity. The attachment of polyethylene glycol chains to interferon has improved its plasma half-life (i.e. reduced the rate at which the body removes the antibody from the bloodstream), essentially by reduced renal clearance and lowering opsonisation (protein binding). It is of interest to modify such biological entities with other polymers, particularly those based on phosphorylcholine because of their enhanced haemocompatibility.

In U.S. Pat. No. 6,310,149 ATRP processes are described in which the initiator comprises a functional group which is a derivative of an organic acid. The acid may be a carboxylic acid or alternatively a phosphorus based acid or sulphonic acid. Examples of initiators are esters of various acids. Monomers which are polymerised include methylmethacrylate, styrene, benzylmethacrylate and 2-hydroxyethylmethacrylate. The polymerisations appear to be solvent-free, that is liquid monomer is the liquid medium for the polymerisation reaction.

Wang, J-S, et al in Polym. Mater. Sci. Eng. 73 (1995) 416 to 417 describe the use of bis-functional initiators for ATRP, whereby the residual group derived from the initiator may be used in subsequent reactions. Examples of end groups or precursors thereof are carboxyl groups, hydroxyl groups and cyano groups.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a new process for forming a biologically active conjugate compound comprising a conjugation step in which a biologically active starting material of the general formula I

RL¹-X¹)_(r)   I

is reacted in an amide bond forming step with a reagent of the general formula II

to form an amide-linked conjugate,

in which R is a biologically active moiety;

L¹ is a bond or a divalent organic linker; and

X¹ is —NHR⁶ or —COR⁷, in which R⁶ is hydrogen, C₁₋₆ alkyl, aryl or an amine activating group and R⁷ is hydroxyl or a carboxyl activating group;

X² is selected from the group consisting of a polymer formed from ethylenically unsaturated monomers and joined through a terminal group, Cl, Br, I, OR¹⁰, SR¹⁴, SeR¹⁴, OP(═O)R¹⁴, OP(═O)(OR¹⁴)₂, O—N(R¹⁴)₂ and S—C(═S)N(R¹⁴)₂, where R¹⁰ is alkyl of from 1 to 20 carbon atoms in which each of the hydrogen atoms may be independently replaced by halide, R¹⁴ is aryl or a straight or branched C₁-C₂₀ alkyl group, and where an N(R¹⁴)₂ group is present, the two R¹⁴ groups may be joined to form a 5- or 6-membered heterocyclic ring;

R¹ and R² are each independently selected from the group consisting of H, halogen, C₁-C₂₀ alkyl, C₃-C₈ cycloalkyl, C(═O)R¹⁵, C(═O)NR¹⁶R¹⁷, COCl, OH, CN, C₂-C₂₀ alkenyl, oxiranyl, glycidyl, aryl, heterocyclyl, aralkyl and aralkenyl, in any of which the alkyl, alkenyl or aryl, heterocyclyl or cycloalkyl groups there may be from 1 to 3 substituents selected from the group consisting of hydrogen, hydroxy C₁-C₄ alkoxy, acyloxy, aryl, heterocyclyl, C(═O)R¹⁵, C(═O)NR¹⁶R¹⁷, oxyranyl and glycidyl; R¹⁵ is alkyl of from 1 to 20 carbon atoms, alkoxy of from 1 to 20 carbon atoms, oligo(alkoxy) in which each alkoxy group has 1 to 3 carbon atoms, aryloxy or heterocyclyloxy any of which groups may have substituents selected from optionally substituted alkoxy, oligoalkoxy, amino (including mono- and di-alkyl amino and trialkyl ammonium, which alkyl groups, in turn may have substituents selected from acyl, acyloxy, alkoxy, alkoxycarbonyl, alkenoxycarbonyl, aryl and hydroxy), and hydroxyl groups;

R¹⁶ and R¹⁷ are independently H or alkyl of from 1 to 20 carbon atoms which alkyl groups, in turn may have substituents selected from alkoxy, acyl, acyloxy, alkoxycarbonyl, alkenoxycarbonyl, aryl and hydroxy, or R¹⁶ and R¹⁷ may be joined together to form an alkanediyl group of from 2 to 5 carbon atoms, thus forming a 3- to 6-membered ring.

R³ and R⁴ are independently selected from hydrogen, and C₁₋₆ alkyl or R³ and R⁴ together are ═O or ═NR⁸ where R⁸ is hydrogen or C₁₋₄ alkyl;

R⁵ is a bond, —O—, —S— or a divalent organic group;

L² is a bond or a divalent linker and,

where X¹ is NHR⁶, X³ is COR⁷ and

where X¹ is COR⁷, X³ is NHR⁶ and

r is an integer of at least 1.

In the conjugation reaction an amide bond is formed from the reaction of the carboxyl functionality COR⁷ and the amine functionality —NHR⁶, of X¹ and X³. Known activating agents may be used to assist the formation of the amide bond, such as carbodiimides and/or N-hydroxysuccinimide. Preferably R⁷ is an N-succinimidyloxy group. R⁶ may be a C₁₋₆ alkyl or aryl group, but is preferably hydrogen.

Preferably the conjugation reacting step is carried out in a protic solvent e.g. a lower alkanol and/or, most preferably, water.

Where X² is other than a polymer chain, the amide conjugate product may be used as an initiator for an atom- or group transfer radical polymerisation reaction.

The ethylenically unsaturated monomers used in such a polymerisation may be any which may be codissolved with the amide in a suitable solvent for such a polymerisation, such as an organic or aqueous solvent. The invention is of most utility for polymerising hydrophilic monomers, that is which are soluble in water, lower alkanols (C₁₋₄-alkanols, including glycols) or glycol ethers. The polymerisation is generally conducted in the presence of one of these solvents, in which the monomers are dissolved. Conveniently the solvent includes water.

Suitable monomers have the general formula III

in which R²³ is selected from the group consisting of hydrogen, halogen, C₁₋₄ alkyl and groups COOR²⁷ in which R²⁷ is hydrogen and C₁₋₄ alkyl;

R²⁴ is selected from the group consisting of hydrogen, halogen and C₁₋₄ alkyl;

R²⁵ is selected from the group consisting of hydrogen, halogen, C₁₋₄ alkyl and groups COOR²⁷ provided that R²³ and R²⁵ are not both COOR²⁷; and

R²⁶ is selected from the group consisting of C₁₋₁₀ alkyl, C₁₋₂₀ alkoxycarbonyl, mono- and di-(C₁₋₂₀ alkyl) amino carbonyl, C₆₋₂₀ aryl (including alkaryl), C₇₋₂₀ aralkyl, C₆₋₂₀ aryloxycarbonyl, C₇₋₂₀ -aralkyloxycarbonyl, C₆₋₂₀ arylamino carbonyl, C₇₋₂₀ aralkyl-amino carbonyl, hydroxyl and carboxylic C₂₋₁₀ acyloxy groups, any of which may have one or more substituents selected from the group consisting of halogen atoms, alkoxy, oligo-alkoxy, aryloxy, acyloxy, acylamino, amine (including mono and di-alkyl amino and trialkylammonium in which the alkyl groups may be substituted), carboxyl, sulphonyl, phosphoryl, phosphino, (including mono- and di- alkyl phosphine and tri-alkylphosphonium), zwitterionic, hydroxyl, vinyloxycarbonyl and other vinylic and allylic groups, and reactive silyl and silyloxy groups, such as trialkoxysilyl groups;

or R²⁶ and R²⁵ or R²⁵ and R²³ may together form —CONR²⁸CO in which R²⁸ is a C₁₋₂₀ alkyl group.

It is preferred for at least two of the groups R^(23,) R^(24,) R²⁵ and R²⁶ to be halogen or, more preferably, hydrogen atoms. Preferably R²³ and R²⁴ are both hydrogen atoms. It is particularly preferred that compound of general formula III be a styrene-based or (alk) acrylic based compound. In styrene based compounds R²⁶ represents an aryl group, especially a substituted aryl group in which the substituent is an amino alkyl group, a carboxylate or a sulphonate group. Where the comonomer is an (alk) acrylic type compound, R²⁶ is an alkoxycarbonyl, an alkyl amino carbonyl, or an aryloxy carbonyl group R²³ and R²⁴ are each hydrogen and R²⁵ is hydrogen or C₁₋₄ alkyl. Most preferably in such compounds R²⁶ is a C₁₋₂₀ -alkoxy carbonyl group, optionally having a hydroxy substituent. (Alk) acrylic compounds are generally methacrylic in which case R²⁵ is methyl.

Preferably the monomers include a zwitterionic monomer having the general formula IV

YBX   IV

in which Y is an ethylenically unsaturated group selected from H₂C═CR¹⁷—CO-A-, H₂C═CR¹⁷—C₆H₄-A¹-, H₂C═CR¹⁷—CH₂A¹⁸,

R²O—CO—CR¹⁷═CR¹⁷—CO—O, R¹⁷CH═CH—CO—O—, R¹⁷CH═C(COOR¹⁸)CH₂—CO—O,

A is —O— or NR¹⁹;

A¹ is selected from a bond, (CH₂)_(l)A² and (CH₂)_(l)SO₃— in which l is 1 to 12;

A² is selected from a bond, —O—, O—CO—, CO—O, CO—NR¹—, —NR¹—CO, O—CO—NR¹—, NR¹—CO—O—;

R¹⁷ is hydrogen or C₁₋₄ alkyl;

R¹⁹ is hydrogen, C₁₋₄₋ alkyl or BX;

R¹⁸ is hydrogen or C₁₋₄ alkyl;

B is a bond, or a straight branched alkanediyl, alkylene oxaalkylene, or alkylene (oligooxalkylene) group, optionally containing one or more fluorine substituents; and

X is a zwitterionic group.

Preferably X is an ammonium, phosphonium, or sulphonium phosphate or phosphonate ester zwitterionic group, more preferably a group of the general formula V

in which the moieties A³ and A⁴, which are the same or different, are —O—, —S—, —N— or a valence bond, preferably —O—, and W⁺ is a group comprising an ammonium, phosphonium or sulphonium cationic group and a group linking the anionic and cationic moieties which is preferably a C₁₋₁₂-alkanediyl group,

preferably in which W⁺ is a group of formula

—W¹—N⁺R²⁰ ₃, —W¹—P⁺R²¹ ₃, —W¹—S⁺R²¹ ₂ or —W¹—Het⁺ in which:

W¹ is alkanediyl of 1 or more, preferably 2-6 carbon atoms optionally containing one or more ethylenically unsaturated double or triple bonds, disubstituted-aryl (arylene), alkylene arylene, arylene alkylene, or alkylene aryl alkylene, cycloalkanediyl, alkylene cycloalkyl, cycloalkyl alkylene or alkylene cycloalkyl alkylene, which group W¹ optionally contains one or more fluorine substituents and/or one or more functional groups; and

either the groups R²⁰ are the same or different and each is hydrogen or alkyl of 1 to 4 carbon atoms, preferably methyl, or aryl, such as phenyl, or two of the groups R²⁰ together with the nitrogen atom to which they are attached form an aliphatic heterocyclic ring containing from 5 to 7 atoms, or the three groups R²⁰ together with the nitrogen atom to which they are attached as heteroaromatic ring having 5 to 7 atoms, either of which rings may be fused with another saturated or unsaturated ring to form a fused ring structure containing from 5 to 7 atoms in each ring, and optionally one or more of the groups R²⁰ is substituted by a hydrophilic functional group, and

the groups R²¹ are the same or different and each is R²⁰ or a group OR²⁰, where R²⁰ is as defined above; or

Het is an aromatic nitrogen-, phosphorus- or sulphur-, preferably nitrogen-, containing ring, for example pyridine.

Monomers in which X is of the general formula in which W⁺ is W¹N^(⊕)R²⁰ ₃ may be made as described in our earlier specification WO-A 93/01221. Phosphonium and sulphonium analogues are described in WO-A 95/20407 and WO-A 94/16749.

Generally a group of the formula V has the preferred general formula VI

where the groups R²² are the same or different and each is hydrogen or C₁₋₄ alkyl, and m is from 1 to 4, in which preferably the groups R²² are the same preferably methyl.

In phosphobetaine based groups, X may have the general formula VII

in which A⁵ is a valence bond, —O—, —S— or —NH—, preferably —O—;

R⁹ is a valence bond (together with A⁵) or alkanediyl, —C(O)alkylene- or —C(O)NH alkylene preferably alkanediyl, and preferably containing from 1 to 6 carbon atoms in the alkanediyl chain;

W² is S, PR³⁰ or NR³⁰;

the or each group R³⁰ is hydrogen or alkyl of 1 to 4 carbon atoms or the two groups R³⁰ together with the heteroatom to which they are attached form a heterocyclic ring of 5 to 7 atoms;

R³¹ is alkanediyl of 1 to 20, preferably 1 to 10, more preferably 1 to 6 carbon atoms;

A⁶ is a bond, NH, S or O, preferably O; and

R³² is a hydroxyl, C₁₋₁₂ alkyl, C₁₋₁₂ alkoxy, C₇₋₁₈ aralkyl, C₇₋₁₈ -aralkoxy, C₆₋₁₈ aryl or C₆₋₁₈ aryloxy group.

Monomers comprising a group of the general formula VII may be made by methods as described in JP-B-03-031718, in which an amino substituted monomer is reacted with a phospholane.

In compounds comprising a group of the general formula VII, it is preferred that

A⁵ is a bond;

R²⁹ is a C₂₋₆ alkanediyl;

W² is NR⁷:

each R⁷ is C₁₋₄ alkyl;

R³¹ is C₂₋₆ alkanediyl;

A⁶ is O; and

R³² is C₁₋₄ alkoxy.

Alternatively X may be a zwitterion in which the anion comprises a sulphate, sulphonate or carboxylate group.

One example of such a group is a sulphobetaine group, of the general formula VIII

where the groups R³³ are the same or different and each is hydrogen or C₁₋₄ alkyl and s is from 2 to 4.

Preferably the groups R³³ are the same. It is also preferable that at least one of the groups R³³ is methyl, and more preferable that the groups R³³ are both methyl.

Preferably s is 2 or 3, more preferably 3.

Another example of a zwitterionic group having a carboxylate group is an amino acid moiety in which the alpha carbon atom (to which an amine group and the carboxylic acid group are attached) is joined through a linker group to the backbone of the biocompatible polymer. Such groups may be represented by the general formula IX

in which A⁷ is a valence bond, —O—, —S— or —NH—, preferably —O—,

R³⁴ is a valence bond (optionally together with A⁷) or alkanediyl, —C(O)alkylene- or —C(O)NHalkylene, preferably alkanediyl and preferably containing from 1 to 6 carbon atoms; and

the groups R³⁵ are the same or different and each is hydrogen or alkyl of 1 to 4 carbon atoms, preferably methyl, or two or three of the groups R³⁵, together with the nitrogen to which they are attached, form a heterocyclic ring of from 5 to 7 atoms, or the three group R³⁵ together with the nitrogen atom to which they are attached form a fused ring heterocyclic structure containing from 5 to 7 atoms in each ring.

Another example of a zwitterion having a carboxylate group is a carboxy betaine —N^(⊕)(R³⁶)₂(CH₂)_(u)COO— in which the R³⁶ groups are the same or different and each is hydrogen or C₁₋₄ alkyl and u is 2 to 6, preferably 2 or 3.

In the zwitterionic monomer of the general formula IV it is preferred that the ethylenic unsaturated group Y is H₂C═CR¹⁷—CO-A-. Such (alk) acrylic moieties are preferably methacrylic, that is in which R¹⁷ is methyl, or acrylic, in which R¹⁷ is hydrogen. Whilst the compounds may be (alk)acrylamido compounds, that is in which A is NR¹⁹, in which case R¹⁹ is preferably hydrogen, or less preferably, methyl, most preferably the compounds are esters, that is in which A is O.

In monomers of the general formula IV, especially where Y is the preferred (alk)acrylic group, B is most preferably an alkanediyl group. Whilst some of the hydrogen atoms of such group may be substituted by fluorine atoms, preferably B is an unsubstituted alkanediyl group, most preferably a straight chain group having 2 to 6 carbon atoms.

A particularly preferred zwitterionic monomer is 2-methacryl-oyloxyethyl-2′-trimethylammonium ethyl phosphate inner salt (MPC).

Another suitable monomer is a compound which is a mono-, di-, or oligo-hydroxy C₂₋₆ alkyl(alk) acrylate or -(alk) acrylamide, an oligo (ethoxy) alkyl(alk)acrylate or acrylamide or a N,N-dimethyl(alk)acrylamide.

Where X² is a polymer chain the reagent of the general formula II may be made in a preliminary polymerisation step in which ethylenically unsaturated monomers are polymerised in the presence of an initiator of the general formula XI

in which X³, L² and R¹ to R⁵ are as defined in relation to general formula II and X⁴ is selected from the group consisting of Cl, Br, I, OR⁵¹, SR⁵², SeR⁵², OP(═O)R⁵², OP(═O)(OR⁵²)₂, O—N(R⁵²)₂ and S—C(═S)N(R⁵²)₂, where R⁵¹ is alkyl of from 1 to 20 carbon atoms in which each of the hydrogen atoms may be independently replaced by halide, R⁵² is aryl or a straight or branched C₁-C₂₀ alkyl group, and where an N(R⁵²)₂ group is present, the two R⁵² groups may be joined to form a 5- or 6-membered heterocyclic ring.

In this atom or group transfer radical polymerisation process the ethylenically unsaturated monomers which are polymerised may be of the same type as are described above in relation to polymerisation processes in which the amide conjugate is used as the initiator.

A group or atom transfer radical polymerisation is carried out in the presence of a catalyst, which comprises a transition metal salt and a ligand. The transition metal compound which comprises a component of the catalyst is M_(q) ^(n+)X⁵ _(q), where:

M_(t) ^(q+) may be selected from the group consisting of Cu¹⁺, Cu²⁺, Fe²⁺, Fe³⁺, Ru²⁺, Ru³⁺,Cr²⁺, Cr³⁺, Mo²⁺, Mo³⁺, W²⁺, W³⁺, Mn²⁺, Mn³⁺, Mn⁴⁺, Rh³⁺, Rh⁴⁺, Re²⁺, Re³⁺, Co⁺, Co²⁺, Co³⁺, V²⁺, V³⁺, Zn⁺, Zn²⁺, Ni²⁺, Ni³⁺, Au⁺, Au²⁺, Ag⁺ and Ag²⁺;

X⁵ is selected from the group consisting of halogen, C₁-C₆-alkoxy, (SO₄)_(1/2), (PO₄)_(1/3), (R¹⁸PO₄)½, (R¹⁸ ₂PO₄), triflate, hexafluorophosphate, methanesulphonate, arylsulphonate, CN and R¹⁹CO₂, where R¹⁸ is aryl or a straight or branched C₁₋₂₀ alkyl and R¹⁹ is H or a straight or branched C₁-C₆ alkyl group which may be substituted from 1 to 5 times with a halogen; and

q is the formal charge on the metal (0≦n≦7).

Preferably X⁵ is halide, most preferably chloride or bromide. Particularly suitable transition metal compounds are based on copper or ruthenium, for instance CuCl or RuCl₂.

In the catalyst, the ligand is preferably selected from the group consisting of:

a) compounds of the formulas:

R³⁷—Z—R³⁸

and

R³⁷—Z—(R³⁹—Z)_(p)—R³⁸

where:

R³⁷ and R³⁸ are independently selected from the group consisting of H, C₁-C₂₀ alkyl, aryl, heterocyclyl and C₁-C₆ alkoxy, C₁-C₄ dialkylamino, C(═O)R⁴⁰, C(═O)R⁴¹R⁴² and A⁸C(═O)R⁴³, where A⁸ may be NR⁴⁴ or O; R⁴⁰ is alkyl of from 1 to 20 carbon atoms, aryloxy or heterocyclyloxy; R⁴¹ and R⁴² are independently H or alkyl of from 1 to 20 carbon atoms or R⁴¹ and R⁴² may be joined together to form an alkanediyl group of from 2 to 5 carbon atoms, thus forming a 3- to 6-membered ring; R⁴³ is H, straight or branched C₁-C₂₀ alkyl or aryl and R⁴⁴ is hydrogen, straight or branched C₁₋₂₀-alkyl or aryl; or R³⁷ and R³⁸ may be joined to form, together with Z, a saturated or unsaturated ring;

Z is O, S, NR⁴⁵ or PR⁴⁶, where R⁴⁶ is selected from the same group as R³⁷ and R³⁸, and where Z is PR⁴⁶, R⁴⁶ can also C₁-C₂₀ alkoxy or Z may be a bond, CH₂ or a fused ring, where one or both of R³⁷ and R³⁸ is heterocyclyl,

each R³⁹ is independently a divalent group selected from the group consisting of C₁-C₈ cycloalkanediyl, C₁-C₈ cycloalkanediyl, arenediyl and heterocyclylene where the covalent bonds to each Z are at vicinal positions or R³⁹ may be joined to one or both of R³⁷ and R³⁸ to formulate a heterocyclic ring system; and

p is from 1 to 6;

b) CO;

c) porphyrins and porphycenes, which may be substituted with from 1 to 6 halogen atoms, C₁₋₆ alkyl groups, C₁₋₆-alkoxy groups, C₁₋₆ alkoxycarbonyl, aryl groups, heterocyclyl groups, and C₁₋₆ alkyl groups further substituted with from 1 to 3 halogens;

d) compounds of the formula R⁴⁷R⁴⁸C(C(═O)R⁴⁹)₂, where R⁴⁹ is C₁₋₂₀ alkyl, C₁₋₂₀ alkoxy, aryloxy or heterocyclyloxy; and each of R⁴⁷ and R⁴⁸ is independently selected from the group consisting of H, halogen, C₁₋₂₀ alkyl, aryl and heterocyclyl, and R⁴⁷ and R⁴⁸ may be joined to form a C₁₋₈ cycloalkyl ring or a hydrogenated aromatic or heterocyclic ring, of which the ring atoms may be further substituted with 1 to 5 C₁₋₆ alkyl groups, C₁₋₆ alkoxy groups, halogen atoms, aryl groups, or combinations thereof; and

e) arenes and cyclopentadienyl ligands, where said cyclopentadienyl ligand may be substituted with from one to five methyl groups, or may be linked through and ethylene or propylene chain to a second cyclopentadienyl ligand.

Selection of a suitable ligand is, for instance, based upon the solubility characteristics and/or the separability of the catalyst from the product polymer mixture. Generally the catalyst is soluble in the liquid reaction mixture, although under some circumstances it may be possible to immobilise the catalyst, for instance on a porous substrate. For the preferred process, which is carried out in the liquid phase, the ligand is soluble in a liquid phase. The ligand is generally a nitrogen containing ligand. The preferred ligand may be a compound including a pyridyl group and an imino moiety, such as bipyridine, or

where R⁵⁰ is a suitable alkyl group, the substituent being variable and adaptable to confer desired solubility characteristics or may be triphenylphosphine or 1,1,4,7,10,10-hexamethyl-triethylene tetramine.

Such nitrogen-containing ligands are usefully used in combination with copper (I) chloride, copper (I) bromide or ruthenium chloride transition metal compounds as part of the catalyst.

The atom or group transfer radical polymerisation process of the invention is preferably carried out to achieve a degree of polymerisation in the range 2 to 100. Preferably the degree of polymerisation is in the range 5 to 50, more preferably in the range 10 to 25. In the preferred group or atom transfer radical polymerisation technique, the degree of polymerisation is directly related to the initial ratios of initiator to monomer. Preferably the ratio is in the range 1:(2 to 100), more preferably in the range of 1:(5 to 50), most preferably in the range 1:(10 to 25).

The ratio of metal compound and ligand in the catalyst should be approximately stoichiometric, based on the ratios of the components when the metal ion is fully complexed. The ratio should preferably be in the range 1:(0.5 to 2) more preferably in the range 1:(0.8 to 1.25). Preferably the range is about 1:1.

In the process, the catalyst may be used in amounts such that a molar equivalent quantity as compared to the level of initiator is present. However, since catalyst is not consumed in the reaction, it is generally not essential to include levels of catalyst as high as of initiator. The ratio of catalyst (based on transition metal compound) to initiator is preferably in the range 1:(1 to 50), more preferably in the range 1:(1 to 10).

In the invention R⁵ is, for instance, a group joined to the carbon atom to which R³ and R⁴ are joined through an oxygen atom, a group —NR⁸— where R⁸ is hydrogen or C₁₋₄ alkyl, a carboxyl (provided that R³ and R⁴ together are not ═O) or a alkyl carbon atom or aryl carbon atom. It may additionally comprise an alkanediyl group, cycloalkane-diyl, an oligo(alkoxy) alkyl, arylene or alkarylene group. At the end joined to L² it may comprise —O—, —S—, —CO— or NR⁸ or may be joined to L² through an aromatic or aliphatic carbon atom.

Linkers L¹ and/or L² may comprise, for instance, the residue of a bifunctional linking reagent such as an oligo peptide, a compound having two similar functionalities, such as isocyanates epoxides hydroxyl, thiols, amines, carboxyls, aldehydes, or two different functionalities selected from the same list. Preferably where L¹ and/or L² is other than a bond, it is the residue of a hetero-bifunctional linking reagent especially a reagent comprising one carboxylic functionality and an amide, hydroxy or phenol functionality.

The invention allows conjugation of an biologically active moiety R to a polymer or initiator precursor of a polymer, using well understood conjugation reactions, which may be carried out under relatively mild conditions and with high efficiency, to form conjugates having controllable solubility, bioavailability, stability or delivery and targeting characteristics. For instance protein actives may be rendered more stable by conjugation to hydrophilic polymers, especially polymers having pendant zwitterionic groups. The active may, for instance be an antibody or fragment thereof, a cytokine, such as an integer or, a peptide therapeutic, a hormone, an enzyme. The polymer conjugated moiety may be cleavable after delivery, for instance where it is conjugated at an active site, or may be substantially non-cleavable provided the activity of the biologically active compound is not deleteriously affected. The biologically active moiety may be linked to L¹X¹ through functional pendant groups or terminal groups. On peptides the pendant groups may be side chains on amino acyl residues, especially amine, hydroxyl thiol or carboxyl groups. Similarly, on such compounds the terminal groups are amino groups or carboxyl groups. Since r may be greater than 1, this indicates that more than one of the potentially reactive functional pendant or terminal groups may be provided with L¹X¹ groups for subsequent conjugation.

Preliminary steps of attaching linkers and groups X¹ to biologically active molecules, including methods for controlling the site of the attachment, by suitable protection and activation strategies, are known and may be used herein.

The present invention also provides a conjugate of the general formula XII

where B¹ is —CONR⁶— or —NR⁶—CO—

t is in the range 1 to r; and

R, L¹, L², R¹ to R⁵ and X² are as defined above, as well as compositions comprising the compound and the compound for use in a method of treatment or diagnosis. The value of t may be an integer but need not be an integer as it will represent the average level of derivatisation across the population. Where t=r the biologically active molecule is fully derivatised.

The compound of formula XII, especially where it contains a linker L¹ or L², may be formed in an alternative sequence of steps in which the biologically active compound is conjugated to an intermediate reagent by a process other than amide bond formation. For instance the intermediate may be formed in a preliminary reaction in which the bond B¹ is formed. An example is described below in Example 4. The process of the first aspect of the invention is the preferred route for synthesising XII.

The invention also provides a polymerisation process in which ethylenically unsaturated monomers are polymerised by atom or group radical transfer polymerisation in the presence of an initiation selected from 4-(3-(2-bromo, 2-methyl-propionate)phenyl)-propionic acid N-hydroxysuccinimide ester and 2-bromo, 2-methyl-propionic acid N-hydroxysuccinimide ester. The monomers in the polymerisation are preferably as defined above in relation to the first aspect of the invention. The polymerisation is conducted in the same preferred solvents, preferably including water.

The compound 2-bromo, 2-methyl-propionic acid N-hydroxysuccinimide ester is believed to be a new compound and is thus claimed herein.

Polymer—biologically active compound conjugates may be useful pharmaceuticals eg as the compound may be a prodrug. The conjugation may be used to control the solubility biological availability, stability, immunogenicity or other physical, chemical or biological characteristics of the biologically active compound.

The invention is illustrated in the following examples:

in which we describe a method by which the 2-bromo, 2-methyl propionic acid bromide can be converted in the first instance to a water-soluble and reactive analogue that can be subsequently used to modify biological entities in aqueous media in order to prepare initiators for ATRP. The aqueous-reactive initiator can be attached to the biological molecule and then the entire entity used to initiate ATRP in water, or alternatively, the reactive initiator itself can be used to grow a polymer chain with a reactive functionality, which can be subsequently reacted with the biological entity in a later reaction to form the polymer-modified molecule.

EXAMPLE 1 a Preparation of 4-(3-(2-bromo, 2-methyl-propionate)phenyl)-propionic acid N-hydroxysuccinimide ester

To a solution of 4-(3-hydroxyphenyl)-propionic acid (a) in acetonitrile, TMEDA (0.55 equiv) is added and stirred at room temperature for about 5 min. A solution of 2-bromo, 2-methyl propionic acid bromide (b) (1.5 equivalent) in acetonitrile is slowly added. After about 15 min of addition a white precipitate should be observed in the reaction vessel. After addition of the acid bromide (about 30 min), the reaction was stirred for a further 60 min approximately. The reaction mixture is filtered and the solvent was removed in vacuo to yield 4-(3-(2-bromo, 2-methyl-propionic ester)phenyl)-propionic acid (c).

To a solution of 4-(3-(2-bromo, 2-methyl-propionate)phenyl)-propionic acid (1 equivalent) in THF, N-hydroxy succinimde (1.05 equivalents) and dicyclohexylcarbodi-imide (d) (1.05 equivalents) is added at −18° C. and stirred for about 2 h. The reaction was allowed to warm to room temperature and stirred for a further 10 h approximately. The reaction is worked up as described by Rutinger & Ruegg in Biochem J., 133(3), 538, 1973 to yield 4-(3-(2-bromo, 2-methyl-propionate)phenyl)-propionic acid

N-hydroxysuccinimide ester (e).

EXAMPLE 1b Preparation of 2-bromo, 2-methyl-propionic acid N-hydroxysuccinimide ester

To a solution of 2-bromo, 2-methyl-propionic acid (a1) (1 equivalent) in THF, N-hydroxy succinimde (1.05 equivalents) and dicyclohexylcarbodi-imide (d) (1.05 equivalents) is added at −18° C. and stirred for about 2 h. The reaction is allowed to warm to room temperature and stirred for about a further 10 h. The reaction is worked up as described by Rutinger & Ruegg in Biochem J., 133(3), 538, 1973 to yield 2-bromo, 2-methyl-propionic acid N-hydroxysuccinimide ester (e1).

EXAMPLE 2 ATRP Using a Lysozyme-Modified Initiator

a) To a suspension of 4-(3-(2-bromo, 2-methyl-propionate) phenyl)-propionic acid N-hydroxysuccinimide (e) ester in borate buffer, lysozyme is added and the resulting mixture gently shaken at room temperature for about 8 h. The initiator (f) was used without isolation.

b) The initiator solution is purged with nitrogen for about 30 min, and then copper bromide catalyst and the bipyridyl ligand added. The solution is further purged with nitrogen, and MPC added (50× catalyst concentration, target Mn 15 000). The green reaction mixture was stirred for about 8 h at room temperature. The reaction is monitored by NMR aliquots, for consumption of the MPC methacrylate groups. The reaction mixture is analysed and product (g) purified by Capillary Electrophoresis. The conjugated lysozyme may be tested for its activity by a standard assay.

EXAMPLE 3 ATRP using the 4-(3-(2-bromo-2-methyl-propionate)phenyl)-propionic acid N-hydroxysuccinimide ester

a) The initiator solution (4-(3-(2-bromo-2-methyl-propionate)phenyl)-propionic acid N-hydroxysuccinimide ester (e) in methanol) is purged with nitrogen for about 30 min, and then copper bromide catalyst and the bipyridyl ligand added. The solution was further purged with nitrogen, and MPC added (50× catalyst concentration, target Mn 15 000). The green reaction mixture is stirred for about 8 h at room temperature. The reaction is monitored by NMR aliquots, for consumption of the MPC methacrylate groups. The reaction mixture is purified on a silica gel column to yield 4-(3-(2-poly-Pm, 2-methyl-propionate)phenyl)-propionic acid N-hydroxysuccinimide ester (h).

b) To a suspension of 4-(3-(2-poly-Pm, 2-methyl-propionate)phenyl)-propionic acid N-hydroxysuccinimide ester in borate buffer, lysozyme is added and the resulting mixture stirred at room temperature for about 12 h. The reaction mixture is again analysed and the product (g) purified by Capillary Electrophoresis. The activity of the conjugated lysozyme may be determined by a standard assay.

EXAMPLE 4 N-butyraldehyde 2-bromoisobutylamide

To 100 ml of dry THF, 8.1 g (0.05 mol) 4-aminobutyraldehyde diethyl acetal and 8.4 ml (0.06 mol) triethylamine were added. The reaction flask was kept in ice-water bath, and 2-bromoisobutyryl bromide (7.5 ml, 0.06 mol) was added dropwise by a syringe over 30 min. The reaction was then stirred for 2 hours at room temperature. The white amine halide salt precipitate was filtered off by Buchner funnel. After evaporating half of the THF under reduced pressure, the filtered THF solution was treated with 25 ml of 20% trifluoroacetic acid aqueous solution overnight to cleave the diethyl acetal protection group. The mixture was neutralised by addition of 5% of NaHCO₃ water solution to pH 8, and the product aldehyde was extracted three times by 50 ml DCM each time. After evaporation of DCM, a red-yellow liquid was obtained. Further purification was carried out by silicon column using DCM as eluent. The final product is colorless liquid, and stored at −20° C. freezer.

The product may be conjugated to lysozyme by a reductive amination process in which a Schiff base is formed. This general technique is known for derivatising proteins having available primary amine groups. 

1. A polymerisation process in which ethylenically unsaturated monomers are polymerised by atom or group radical transfer polymerisation in the presence of an initiator selected from 4-(3-(2-bromo, 2-methyl-propionate)phenyl)-propionic acid N-hydroxysuccinimide ester and 2-bromo, 2-methyl-propionic acid N-hydroxysuccinimide ester to form a polymer product having an N-hydroxysuccinimide ester terminal group.
 2. A polymerisation process according to claim 1 in which the ethylenically unsaturated monomers have the general formula Ill

in which R²³ is selected from the group consisting of hydrogen, halogen, C₁₋₄ alkyl and groups COOR²⁷ in which R²⁷ is hydrogen and C₁₋₄ alkyl; R²⁴ is selected from the group consisting of hydrogen, halogen and C₁₋₄ alkyl; R²⁵ is selected from the group consisting of hydrogen, halogen, C₁₋₄ alkyl and groups COOR²⁷ provided that R²³ and R²⁵ are not both COOR²⁷; and R²⁶ is selected from the group consisting of C₁₋₁₀ alkyl, C₁₋₂₀ alkoxycarbonyl, mono- and di-(C₁₋₂₀ alkyl) amino carbonyl, C₆₋₂₀ aryl, C₇₋₂₀ aralkyl, C₆₋₂₀ aryloxycarbonyl, C₇₋₂₀ -aralkyloxycarbonyl, C₆₋₂₀ arylamino carbonyl, C₇₋₂₀ aralkyl-amino carbonyl, hydroxyl and C₂₋₁₀ acyloxy groups, any of which may have one or more substituents selected from the group consisting of halogen atoms, alkoxy, oligo-alkoxy, aryloxy, acyloxy, acylamino, amine carboxyl, sulphonyl, phosphoryl, phosphino zwitterionic groups, hydroxyl, vinyloxycarbonyl and other vinylic and allylic groups, and reactive silyl and silyloxy groups; or R²⁶ and R²⁵ or R²⁵ and R²³ may together form —CONR²⁸CO in which R²⁸ is a C₁₋₂₀ alkyl group.
 3. A process according to claim 1 carried out in the presence of water.
 4. A process according to claim 1 in which the polymer product is reacted with an amine-group containing protein in an amide-bond forming reaction wherein the said N-hydroxysuccinimide ester group reacts with the said amine group, to form an amide conjugate.
 5. 2-bromo-2-methyl-propionic acid N-hydroxysuccinimide ester. 